Periodic Reporting for period 2 - ATTIDA (Attosecond space-time imaging of coherent quantum dynamics)
Periodo di rendicontazione: 2021-07-01 al 2022-12-31
Electron motion is at the heart of matter, technology and life and evolves on an extremely fast time scale known as the attosecond time scale (1 attosecond = 10^-18 seconds). In systems with a finite size, such as molecules and nanomaterials, this motion is in addition confined to spatial scales on the order of nanometers or less. This confinement enhances quantum effects and gives rise to dynamics involving a multitude of electrons. These dynamics are coherent, which means that they evolve according to the quantum wave nature of the electrons. However, the coherent effects last only up to tens of thousands of attoseconds due to the influence of the environment, making their detection very challenging. In order to observe these phenomena simultaneously in space and time, a new methodology is required. In this project, we will address this challenge by developing two electron microscopy methods, attosecond scanning tunneling microscopy (STM) and ultrafast low-energy electron holography (LEEH). In attosecond STM, a pair of extremely short laser pulses illuminate a sample, such as an organic molecule. The first pulse excites the molecule at a specific atomic spot and creates coherent multi-electron dynamics. The second pulse probes the system and creates an attosecond snapshot of the electron dynamics at the same atomic spot. In the second method, ultrafast LEEH, we use a beam consisting of extremely short electron pulses to probe electron dynamics inside a nanomaterial sample. The interaction with electrons inside the sample is imprinted on the electron beam, resulting in a holographic image on a screen. Both methods will allow us to record movies of the coherent electron dynamics, their evolution in space and time, and also to follow their demise. Our research will not only allow us to take a look into new physics at extremely short time scales, but has also implications for technology where light and multiple electrons are involved, such as photovoltaic cells or chemical reactions.
Within the first reporting period, the project ATTIDA was initiated at the Technion - Israel Institute of Technology. A team of physicists was formed to carry out the proposed research in our new laboratory. We have successfully designed constructed a suitable experimental setup for attosecond STM. In first experiments, we are exploring the physics underlying the interaction of an ultrashort laser pulse with a flat metallic test sample. Aided by a novel measurement method for laser-driven currents based on fast light modulation, we have achieved proof-of-principle demonstrations of some of the main ingredients of attosecond STM, tunneling and high spatial resolution. Both are indispensable for the realization of attosecond STM as a novel method. Furthermore, we have realized a source of ultrashort electron pulses for ultrafast LEEH inside a dedicated experimental setup placed in ultrahigh vacuum. This work has been presented at the METANANO 2021 conference (Michael Krüger, "Ultrafast low-energy electron microscopy of plasmonic fields"). A theory investigation shows that record-short electron pulses with a duration of a few thousand attoseconds are expected at the point of interaction with a nanomaterial sample, which promises excellent temporal resolution. The theory work was reported in a recent publication (Maor Eldar et al., J. Phys. B 55, 074001 (2022), https://doi.org/10.1088/1361-6455/ac5e09). The full implementation of both methods and their respective project objectives is in progress.
In the first period, we significantly progressed beyond the state of the art by the demonstration a novel measurement method for attosecond STM based on fast light modulation. Moreover, we successfully realized laser-driven electron tunneling on the nanoscale. With a further development of the system, which includes significant improvements to the laser systems, we expect that the generation and control of attosecond currents can be achieved in the attosecond STM setup. A dedicated source of attosecond light pulses, currently being designed, and the introduction of molecular samples will enable excitation and imaging of ultrafast coherent electron dynamics. Also towards the second method, ultrafast LEEH, we have made significant progress beyond prior research. Our pulsed electron source supports a temporal resolution far better than the state of the art, which will enable insights into ultrafast charge dynamics in nanomaterials. The full setup for ultrafast LEEH is currently under development. We expect that our method can be applied to a wide range of systems and phenomena.